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      <a id="tempest"></a>
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        <h2>
          <span class="refentrytitle">tempest</span>
        </h2>
        <p>tempest — 
      Estimate the tempo of beat patterns in a control signal.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp157977168"></a>
        <h2>Description</h2>
        <p>
      Estimate the tempo of beat patterns in a control signal.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp157978320"></a>
        <h2>Syntax</h2>
        <pre class="synopsis">ktemp <span class="command"><strong>tempest</strong></span> kin, iprd, imindur, imemdur, ihp, ithresh, ihtim, ixfdbak, \
      istartempo, ifn [, idisprd] [, itweek]</pre>
      </div>
      <div class="refsect1">
        <a id="idp157980528"></a>
        <h2>Initialization</h2>
        <p>
      <span class="emphasis"><em>iprd</em></span> -- period between analyses (in seconds). Typically about .02 seconds.
    </p>
        <p>
      <span class="emphasis"><em>imindur</em></span> -- minimum duration (in seconds) to serve as a unit of tempo. Typically about .2 seconds.
    </p>
        <p>
      <span class="emphasis"><em>imemdur</em></span> -- duration (in seconds) of the <span class="emphasis"><em>kin</em></span> short-term memory buffer which will be scanned for periodic patterns. Typically about 3 seconds.
    </p>
        <p>
      <span class="emphasis"><em>ihp</em></span> -- half-power point (in Hz) of a low-pass filter used to smooth input <span class="emphasis"><em>kin</em></span> prior to other processing. This will tend to suppress activity that moves much faster. Typically 2 Hz.
    </p>
        <p>
      <span class="emphasis"><em>ithresh</em></span> -- loudness threshold by which the low-passed <span class="emphasis"><em>kin</em></span> is center-clipped before being placed in the short-term buffer as tempo-relevant data. Typically at the noise floor of the incoming data.
    </p>
        <p>
      <span class="emphasis"><em>ihtim</em></span> -- half-time (in seconds) of an internal forward-masking filter that masks new <span class="emphasis"><em>kin</em></span> data in the presence of recent, louder data. Typically about .005 seconds.
    </p>
        <p>
      <span class="emphasis"><em>ixfdbak</em></span> -- proportion of this unit's <span class="emphasis"><em>anticipated value</em></span> to be mixed with the incoming <span class="emphasis"><em>kin</em></span> prior to all processing. Typically about .3.
    </p>
        <p>
      <span class="emphasis"><em>istartempo</em></span> -- initial tempo (in beats per minute). Typically 60.
    </p>
        <p>
      <span class="emphasis"><em>ifn</em></span> -- table number of a stored function (drawn left-to-right) by which the short-term memory data is attenuated over time.
    </p>
        <p>
      <span class="emphasis"><em>idisprd</em></span> (optional) -- if non-zero, display the short-term past and future buffers every <span class="emphasis"><em>idisprd</em></span> seconds (normally a multiple of <span class="emphasis"><em>iprd</em></span>). The default value is 0 (no display).
    </p>
        <p>
      <span class="emphasis"><em>itweek</em></span> (optional) -- fine-tune adjust this unit so that it is stable when analyzing events controlled by its own output. The default value is 1 (no change).
    </p>
      </div>
      <div class="refsect1">
        <a id="idp157994992"></a>
        <h2>Performance</h2>
        <p>
<span class="emphasis"><em>tempest</em></span> examines <span class="emphasis"><em>kin</em></span> for amplitude periodicity, and estimates a current tempo. The input is first low-pass filtered, then center-clipped, and the residue placed in a short-term memory buffer (attenuated over time) where it is analyzed for periodicity using a form of autocorrelation. The period, expressed as a <span class="emphasis"><em>tempo</em></span> in beats per minute, is output as <span class="emphasis"><em>ktemp</em></span>. The period is also used internally to make predictions about future amplitude patterns, and these are placed in a buffer adjacent to that of the input. The two adjacent buffers can be periodically displayed, and the predicted values optionally mixed with the incoming signal to simulate expectation.
    </p>
        <p>
This unit is useful for sensing the metric implications of any k-signal (e.g.- the RMS of an audio signal, or the second derivative of a conducting gesture), before sending to a <a class="link" href="tempo.html" title="tempo"><em class="citetitle">tempo</em></a> statement.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp158000048"></a>
        <h2>Examples</h2>
        <p>
      Here is an example of the tempest opcode. It uses the file <a class="ulink" href="examples/tempest.csd" target="_top"><em class="citetitle">tempest.csd</em></a>, and <a class="ulink" href="examples/beats.wav" target="_top"><em class="citetitle">beats.wav</em></a>.
      </p>
        <div class="example">
          <a id="idp158002752"></a>
          <p class="title">
            <strong>Example 921. Example of the tempest opcode.</strong>
          </p>
          <div class="example-contents">
            <p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
            <pre class="programlisting">
<span class="csdtag">&lt;CsoundSynthesizer&gt;</span>
<span class="csdtag">&lt;CsOptions&gt;</span>
<span class="comment">; Select audio/midi flags here according to platform</span>
<span class="comment">; Audio out   Audio in</span>
-odac           -iadc    <span class="comment">;;;RT audio I/O</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o tempest.wav -W ;;; for file output any platform</span>
<span class="csdtag">&lt;/CsOptions&gt;</span>
<span class="csdtag">&lt;CsInstruments&gt;</span>

<span class="comment">; Initialize the global variables.</span>
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">kr</span> <span class="op">=</span> 4410
<span class="ohdr">ksmps</span> <span class="op">=</span> 10
<span class="ohdr">nchnls</span> <span class="op">=</span> 1

<span class="comment">; Instrument #1.</span>
<span class="oblock">instr</span> 1
  <span class="comment">; Use the "beats.wav" sound file.</span>
  asig <span class="opc">soundin</span> "beats.wav"
  <span class="comment">; Extract the pitch and the envelope.</span>
  kcps, krms <span class="opc">pitchamdf</span> asig, 150, 500, 200

  iprd <span class="op">=</span> 0.01
  imindur <span class="op">=</span> 0.1
  imemdur <span class="op">=</span> 3
  ihp <span class="op">=</span> 1
  ithresh <span class="op">=</span> 30
  ihtim <span class="op">=</span> 0.005
  ixfdbak <span class="op">=</span> 0.05
  istartempo <span class="op">=</span> 110
  ifn <span class="op">=</span> 1

  <span class="comment">; Estimate its tempo.</span>
  k1 <span class="opc">tempest</span> krms, iprd, imindur, imemdur, ihp, ithresh, ihtim, ixfdbak, istartempo, ifn
  <span class="opc">printk2</span> k1

  <span class="opc">out</span> asig
<span class="oblock">endin</span>


<span class="csdtag">&lt;/CsInstruments&gt;</span>
<span class="csdtag">&lt;CsScore&gt;</span>

<span class="comment">; Table #1, a declining line.</span>
<span class="stamnt">f</span> 1 0 128 16 1 128 1

<span class="comment">; Play Instrument #1 for two seconds.</span>
<span class="stamnt">i</span> 1 0 2
<span class="stamnt">e</span>


<span class="csdtag">&lt;/CsScore&gt;</span>
<span class="csdtag">&lt;/CsoundSynthesizer&gt;</span>
</pre>
          </div>
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        <p><br class="example-break" />

      The tempo of the audio file <span class="quote">“<span class="quote">beats.wav</span>”</span> is 120 beats per minute. In this examples, tempest will print out its best guess as the audio file plays. Its output should include lines like this:
      </p>
        <pre class="screen">
. i1   118.24654
. i1   121.72949</pre>
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